Sweden, the country with the second highest prevalence of type 1 diabetes in the world, could actually have 2-3 times more adolescents and young adults with type 1 diabetes than previously estimated, according to new findings in Diabetologia.

Current estimates in Sweden are based on the Diabetes Incidence Study in Sweden (DISS), which has been around since 1983. The DISS is one of very few registers to record data on adolescents and young adults and therefore findings from the DISS study have had implications for diabetes research and care in many countries. Dr. Araz Rawshani of the Swedish National Diabetes Register, Gothenburg, and colleagues found that the DISS had very low coverage which discards previous findings.

The researchers found that they could more accurately estimate actual numbers by examining the country's Prescribed Drug Register (PDR) and establishing a diagnosis of type 1 diabetes via a patient's prescription medications; men with at least 1 and women with at least 3 prescriptions for insulin were included as having type 1 diabetes if they had not been given oral antidiabetic drugs. Women needed three prescriptions to avoid confusion with gestational diabetes, and oral antidiabetic drugs ruled out a type 1 diabetes diagnosis since these are used in patients with type 2 diabetes.

They then compared the results from the PDR with incidence rates in patients aged 14 and younger in the Swedish Childhood Diabetes Register (SCDR), which has almost all (95-99%) cases in that age group included, and by assessing diabetes type among 18-34 year olds in the National Diabetes Register (NDR). The absolute number of cases in adolescents and young adults aged 18-34 years was found to be 1,217 in the PDR, almost 3 times that originally thought (435 based on the DISS).

The researchers also found that their findings did not back previous research that the incidence is increasing among children and therefore decreasing in the rest of the population. Previous theories have stated that individuals develop disease earlier, but the total number of individuals has not changed. The new study shows that the incidence in adolescents and young adults is 2-3 times higher than previously reported and is actually as high as that reported in children aged 0-4 years. Consequently these previous theories are now being strongly questioned. "Our analysis of the Prescribed Drug Register found that that incidence rates in young people aged 15-34 years were equal to those in children aged 0-4 years," say the authors.

Since all patients with a diagnosis of type 1 diabetes must be entered into the PDR, the researchers say that this should be the ongoing method to determine type 1 diabetes incidence in any future studies. The authors say: "The incidence of type 1 diabetes is 2